A typical shingle comprises an asphalt impregnated heavy paper stock having mineral granules embedded in one face thereof. The shingles are typically cut to a generally rectangular shape and include one or more slits which define separate tabs on each shingle.
The shingles are cut, stacked, and packaged in bundles on a single continuously operating production line. Typically, a wide web of paper stock progresses continuously along a production line at a very high rate of speed through successive stages of impregnating the web with liquid asphalt, coating with mineral granules, cutting the web into appropriately sized shingles, stacking of individual shingles in superposed relation relative to each other, and bundling the stacked shingles together.
During the cutting stage, the coated and continuously moving web is slit into longitudinal strips and these strips are cut transversely to a rectangular size. During the cutting stage, the tabs are formed by cutting out narrow slits extending inwardly from one side edge of a shingle.
The strips into which the web is slit continue to longitudinally move at very high speeds (700-900 feet per minute) along the production line in what will be referred to as individual "lanes". Typically, a shingle production line may have three or more such "lanes"" along which the slit web is advanced. A stacker machine is arranged at one end of each lane for receiving the shingles successively delivered thereto, stacking the shingles in a superposed relation, and forming individual bundles of shingles. The bundles of shingles are automatically removed from the stacking machine and are subsequently wrapped for delivery to a customer.
U.S. Pat. No. 3,205,794 to F. L. Califano et al. discloses a stacking machine which includes a group-assembling and transfer section, and a stack assembling and squaring section. The group-assembling and transfer section includes a pair of rotatable paddle-like elements or starwheels disposed on opposite sides of shingles advanced to the stacking station. Each starwheel includes a series of shingle support flights or shelves that receive and support shingles after they have been individually cut. As the shingles are received they are slid one on top of another to form a stack comprised of a predetermined number of shingles.
After a predetermined number of shingles have been received and stacked at the group assembling and transfer section, the starwheels are rotated to drop the stack of shingles to the stack assembling and squaring section while concurrently presenting another support flight or shelf to receive the next advancing shingle. At the stack assembling and squaring section, the edges of the shingles are aligned relative to each other. The shingles are thereafter transported away from the stacking machine to a wrapping station.
The stacking machine receives fresh shingles which are still soft and have their mineral granules only loosely held thereon. As will be understood, the softness of the shingles impedes alignment of the shingle edges relative to each other at the group assembling section. Moreover, because the shingles are slid over each other at the group-assembling and transfer section, many of the mineral granules are dislodged from the shingle and are deposited on working parts of the stacker machine. These mineral granules accumulate and because of their coarseness quickly cause wear of the moving parts of the stacker machine.
When shingles enter the stacking machine, they travel at several hundred feet per minute. During starwheel rotation the leading edge of the starwheel rotates in a plane generally transverse to the direction of shingle advancement. To avoid damage to the shingles, the starwheels of the stacker machine must, therefore, be rotatably indexed between positions in only the short time interval between adjacent advancing shingles. As will be appreciated, if the starwheels are not sufficiently indexed between positions in a timely manner, the movement of the starwheel will strike an advancing shingle in a manner impeding shingle advancement toward the group assembling and transfer section and, ultimately causing a jam of the production line.
A major concern during operation of a shingle production line is the elimination of any condition that requires a stopping or slowing down of the web or shingles advancing along the line. This can be particularly significant when considering that any of a variety of possible occurrences at any of the numerous stacker machines or on any of the lanes, such as a jam, may require an interruption or halt of an entire six-lane production line simply because of a jam-up or other occurrence in only one of the lanes.
Any attempt at increasing production line speeds requires increases in the already rapid operation of the stacker machine to adjust to the increased number of shingles being presented thereto. Moreover, the stacking machines must be of relatively inexpensive, straightforward, rugged and dependable construction to avoid costly repair shutdowns, and also considering the substantial number of these units needed to accommodate the one or more production lines.